(1) Field of the Invention
The present invention relates generally to tracking systems and, more particularly, to tracking systems and methods for tracking the trajectory and velocity of underwater objects traveling at high speeds.
(2) Description of the Prior Art
The tracking of a high speed (near or above sonic in the water, e.g., in the range of 900 m/sec) underwater projectile with conventional acoustic range systems is impractical. Moreover, the high-speed projectile in relation to the acoustic propagation from the test body creates great difficulty in accurately determining the position from which the acoustic radiation originated.
The following U.S. Patents describe various prior art systems that may be related to projectile tracking or detection systems generally:
U.S. Pat. No. 3,824,463, issued Jul. 16, 1974, to Oehler, discloses a shot cluster velocity measuring apparatus in which the coils through which the shot is to sequentially pass are mounted in axially spaced relation and are electrically connected as frequency determining elements in a high frequency oscillator, the output of which is frequency modulated as the shot cluster passes the coils. An FM discriminator generates an amplitude varying signal representative of the frequency modulation. A differentiating and filtering circuit shapes the discriminator output which is then amplified. The gain of a variable gain amplifier is automatically adjusted to equalize signal amplitude, and a Schmitt trigger produces rectangular pulses. If the pulses out of the trigger are of sufficient duration, they are used to produce “start” and “stop” signals, indicating the passage of the center of mass of the projectile or projectile cluster through the first and second coils, respectively. These signals are then used to control an interval timer which displays the count as a measure of velocity.
U.S. Pat. No. 6,198,694, issued Mar. 6, 2001, to Kroling et al, discloses a method and a device for deciding relative to a chosen reference system, and without contact, the position, direction or speed—or any combination thereof—for a projectile in its flight through a gas towards a given target, the position of the projectile in a first plane that is determined at a certain distance from the target by means of at least three acoustic sensors arranged in a vicinity of the plane. Acoustic sound waves, emanating from a turbulent gas volume extending essentially straight behind the projectile, and/or emanating from a wake or monopole existing essentially straight behind the projectile, are received by means of the acoustic sensors. Time differences for the arrival of the acoustic sound waves to the respective acoustic sensors are measured. The projectile position (x, y; x1, y1) in the first plane is calculated from the time differences. The hit point of the projectile in a target plane through the target is decided with the help of the calculated projectile position in the first plane.
U.S. Pat. No. 6,467,342, issued Oct. 22, 2002, to Gieseke, discloses an apparatus for measuring velocity of a projectile that includes a plurality of break-screens aligned with each other serially and along a line of travel of the projectile, and parallel to each other, and spaced from each other and from a projectile firing device by selected distances. Each break-screen includes a support sheet and an electrically conductive wire mounted on the sheet so as to be interrupted by passage of the projectile through the sheet. A single amplifier is in communication with each of the conductive wires and is adapted to provide an indication as to a change in voltage in each of the break-screens upon passage of the projectile therethrough, and an indication as to time of the passage. A data collection/display apparatus computes therefrom the velocity of the projectile.
U.S. Pat. No. 6,563,302, issued May 13, 2003, to Raposa et al, discloses a device for sensing projectile velocity in an underwater environment. The device includes a plurality of evenly spaced voltage coil members positioned in the path of a projectile. Each voltage coil member includes a support frame having an opening therein and a magnetic coil mounted on the support frame, and a sensing member connected to each support frame. The sensing member includes means for outputting a signal responsive to passage of the projectile through the voltage coil member, and a logic arrangement for determining a difference between passage of the projectile between adjacent ones of said plurality of voltage coil members throughout the run thereof, thereby determining a velocity of the projectile.
For the most part, the above art is not related to tracking underwater high speed objects. The art for underwater high speed objects appears to be limited to measuring the speed of relatively small metallic objects which travel relatively closely to a magnetic pickup. It would be desirable to provide means for determining the trajectory of such objects as well for measuring the speed and/or velocity and/or trajectory of much larger objects. Consequently, those skilled in the art will appreciate the present invention that addresses the above and other problems.